19 April 2012

Doomed

A really unpleasant backwards-compatibility feature of the Windows shell that I wasn't aware of.

It wasn’t until Windows NT 3.5.1 (and then Windows 95 later) that long file names were supported. Prior to this, there were a lot of limitations on what characters could be part of a filename or directory, one of those being a space.

In fact, any space in a shell command execution was seen to be an argument. This made sense at the time so you could issue a command like this:

C:\DOOM\doom.exe -episode 3

That, of course, would start Doom at episode 3. However, when Microsoft switched to Long File Names, it still had to support this type of invocation. So, the way the windows cmd.exe shell works is simple. You pass it a string like this:

C:\Program Files\id Software\Doom\Doom.exe -nomusic

And it will try to execute “C:\Program” as a file, passing it “Files\id Software\Doom\Doom.exe -nomusic” as argument to that executable. Of course, this program doesn’t exist, so it will then try to execute “C:\Program Files\id”, passing it “Software\Doom\Doom.exe -nomusic” as argument. If this doesn’t exist, it will try to execute “C:\Program Files\id Software\Doom\Doom.exe” passing in “-nomusic” as an argument. It would continue this way until a program existed and started, or until the path was depleted and no program was to be found.

About Me

David Gorsline, full-time professional software developer since 1981, currently a part of the Digital Media team at NPR. Resident of Reston (Fairfax County), Virginia, in the suburbs of Washington, D.C. The opinions expressed here are my own and do not necessarily reflect those of my employer or any other organization.